1. Field of the Invention
This invention relates to an electrochemical device which has excellent low-temperature performance and is easy to miniaturize. More particularly, the invention relates to an electrochemical device having a heater to heat a solid electrolyte thereof.
2. Description of the Prior Art
As an example of electrochemical devices using a solid electrolyte, an oxygen sensor for detecting the oxygen concentration of automobile exhaust gas has been used heretofore. To ensure proper operation of the oxygen sensor when the exhaust gas temperature is comparatively low, it has been known to attach a heater to the sensor; for instance, by inserting a heater in a hole of a cylindrical zirconia solid electrolytic cell having one end thereof closed, or attaching a heater, made of a resistive heating element buried in an alumina porcelain, to one side surface of a planar zirconia solid electrolyte cell.
However, the electrochemical device of the prior art has shortcomings in that its assembly structure is so complicated that the device tends to become large, and that, due to the difference in thermal expansion or sintering shrinkage between insulator portion and solid electrolyte portion thereof, the insulator portion and solid electrolyte portion are susceptible to cracks, resulting in a poor reliability.